A first conventional technique will be described. Conventionally, in an automobile having a hood in the front portion thereof, a vehicle hood panel has an outer panel, an inner panel, and other reinforcing members. To highly ensure the rigidity and strength of the vehicle hood panel, the outer panel is joined to the inner panel with a space therebetween.
In the conventional vehicle hood panel, various techniques are proposed to improve the pedestrian protection performance at pedestrian collision while highly ensuring the mechanical performance, such as rigidity.
For instance, JP 2003-205866 A proposes a structure in which a plurality of hat-shaped beads are formed in parallel near the center of the inner panel, thereby ensuring the dent resistance and the stiffness required for the vehicle hood and improving the pedestrian protection performance at pedestrian collision.
To evaluate the pedestrian protection performance, an HIC value calculated by the time waveform of the acceleration at collision is typically used. As the HIC value is lower, the head of a pedestrian is less likely to be injured at collision. Therefore, as described above, a hood structure which lowers the HIC value while ensuring the dent resistance and the stiffness is desired.
In a typical acceleration waveform when a head collides with the vicinity of the center of the hood panel, a first wave occurs when the head comes into contact with the hood panel in the initial stage of collision, and then, a second wave occurs when the hood panel pressed by the head is moved in the vehicle downward direction and comes into contact with the incorporated components, such as an engine, disposed below the panel.
To reduce the HIC value, in particular, it is effective to make the second wave of acceleration smaller. For this, at head collision, it is necessary to absorb the collision energy before the hood panel comes into contact with the incorporated components. It is desirable to sufficiently ensure the gap between the hood panel and the incorporated components.
However, when considering that the components necessary for the automobile are disposed below the hood in the limited space, it is often difficult to sufficiently ensure the gap between the hood panel and the incorporated components.
Therefore, desired is a hood structure in which the first wave of acceleration at head collision is increased to a maximum extent to increase the amount of energy absorption in the initial stage of collision, so that the deformation stroke is reduced or the second wave of acceleration when the hood comes into contact with the incorporated components is made smaller.
As disclosed in JP 2003-205866 A, the beads are formed in parallel in the inner panel. Therefore, the bending rigidity of the inner panel can be improved, the bending deformation of the inner panel at pedestrian head collision can be restrained, and the impact load can be widely distributed in the panel. With this, the area in which the panel is displaced at pedestrian head collision, that is, the inertia weight, is increased. As compared with the inner panel not having the beads, the first wave of acceleration at head collision can thus be larger. In addition, since the hat-shaped beads are easily spread-deformed at contact with the incorporated components, the second wave of acceleration can be smaller.
Therefore, other than, various techniques for providing the beads in the inner panel are proposed. For instance, in JP 2005-96512 A, JP 2008-24185 A, JP 2004-217008 A, and JP 2005-96608 A, the hat-shaped beads are extended in the vehicle front-rear direction. In JP 2005-96512 A, the vertical walls of the beads have a stepped shape. In JP 2008-24185 A, the depth of the bottoms of the beads is changed. In JP 2004-217008 A, a notch is provided between the beads. In addition, in many cases, a child pedestrian collides with the front of the hood panel, and an adult pedestrian collides with the rear of the hood panel. Therefore, JP 2005-96608 A, the hat-shaped beads in the inner panel have different shapes between the front and rear of the vehicle.
In JP 2006-315555 A, the beads are inclined with respect to the vehicle front-rear direction so that the distance between the beads becomes greater toward the vehicle rear side.
The vehicle hood panel has many design requirements to be satisfied, other than the pedestrian protection performance. For instance, at front collision of vehicles, the hood panel is required to be bending-deformed in doglegged shape in side view for absorbing the impact, thereby restraining the panel from entering into the vehicle. In JP 2005-75163 A and JP 2005-239092 A, the beads extended in the vehicle front-rear direction are connected by a different bead (called a crush bead) extended in the vehicle right-left direction, or the adjacent beads are connected by a flange. The hood panel is thus easily bending-deformed at front collision.
In JP 2005-145224 A, JP 2006-273198 A, JP 2009-90935 A, JP 2008-30574 A, and JP 2010-116074 A, the hat-shaped beads are extended in the vehicle right-left direction. The hood panel is thus easily bending-deformed at front collision.
A second conventional technique will be described. In a vehicle, such as an automobile, having a hood in the front portion of the body thereof, the hood has an outer panel, an inner panel disposed on the lower surface side of the outer panel, and a reinforcing member disposed between the outer panel and the inner panel. To ensure the rigidity and strength of the hood itself, the outer panel is joined to the inner panel to take a closed cross-sectional structure with a space therebetween, a plurality of reinforcing members being provided therein.
In recent years, in addition to ensuring of the hood rigidity, dent resistance, and stiffness, the hood panel has been required to reduce the injury value at pedestrian head collision. To evaluate the pedestrian protection performance, the HIC value calculated by the time waveform of the acceleration at collision is typically used. As the HIC value is lower, the head of a pedestrian is less likely to be injured. That is, desired is a hood structure which lowers the HIC value while ensuring the necessary hood strength requirements. In addition, to ensure the degree of freedom of the layout of various function components, such as an engine, disposed below the hood, desired is a hood structure which can reduce the gap between these components and the lower surface of the hood.
In the acceleration waveform at head collision with the hood, typically, a first wave occurs when the head comes into contact with the outer panel of the hood, and then, a second wave of acceleration occurs due to contact with the components disposed below the hood. To reduce the HIC value, it is most effective to make the second wave of acceleration smaller. It is ideal to sufficiently ensure the gap between the bottom surface of the hood and the components disposed therebelow. However, as described above, when considering the desire to reduce the gap, it is also necessary to increase the first wave of acceleration to reduce the energy absorption stroke itself.
To ensure the rigidity of the inner panel itself, a concave portion is provided in substantially annular shape in the outer periphery of the inner panel of the hood. In recent years, the pedestrian protection requirements have been stricter. Even when the head of a pedestrian collides with the vicinity of the concave portion in the inner panel, which is the outer periphery of the hood, it is necessary to ensure the predetermined pedestrian protection performance.
In particular, the required performance for the dent resistance immediately above the lock is stricter on the front side than in other portions of the hood. Typically, the dent reinforcing member is provided near the lock in the concave portion in the inner panel on the hood front side so as to be close to the outer panel, thereby ensuring the stiffness and dent resistance of the outer panel and improving the pedestrian protection performance (JP 4292549 B2 and JP 2007-98963 A).
In the above structure, the dent reinforcing member is joined to the outer panel by mastic. The interval between the support points on the outer panel is shortened, so that deformation of the outer panel alone is restrained. The dent resistance and stiffness can be reduced, and lowering of the first wave of acceleration due to the deformation resistance reduction at head collision can be restrained. In many cases, these structures have the lock reinforcing member to which the striker is joined in the lower surface side of the inner panel, thereby ensuring the strength and rigidity of the lock.
However, since the above structure uses two reinforcing members, the number of components is increased to make the cost higher.
Accordingly, to reduce the number of components, proposed is a structure in which the lock reinforcing member on the lower surface side of the hood is extended upwardly of the vehicle to eliminate the dent reinforcing member and the lock reinforcing member is joined to the outer panel by mastic, thereby ensuring the dent resistance ( JP 2007-185996 A, JP 2008-296793 A, JP 3956833 B2).
However, the lock reinforcing member is required to ensure the strength and rigidity of the lock, and to have a larger plate thickness than the inner panel and the dent reinforcing member. At pedestrian head collision, the leg connecting the joining surface to the outer panel and the lower surface of the inner panel to which the striker is joined is difficult to be bent. The acceleration at head collision is increased to deteriorate the head injury value (HIC value).
Therefore, to ensure the strength and rigidity of the lock and to improve the pedestrian protection performance, proposed is a structure in which a thin wall member is used for the stiffener on the vehicle rear side with which the head of a pedestrian collides, and a thick wall member is used for the portion of the inner panel to which the striker is joined and the striker supporting portion (JP 2007-69643 A, JP 2008-68795 A, and JP 4479844 B2).
However, in such a structure, the number of components is increased to make the cost higher.
Therefore, used partly is a structure in which the lock reinforcing member is joined to the portion of the inner panel on the vehicle lower side, the inner panel thinner than the lock reinforcing member is disposed on the striker, and the inner panel is joined to the outer panel by mastic, thereby ensuring the dent resistance and pedestrian protection performance (JP 3800601 B2, JP 2005-75176 A, JP 2008-247394 A, and JP 4395597 B2).
FIG. 31 is a bottom view showing a conventional vehicle hood. An outer panel 201 is overlapped with and fixed to an inner panel 202. Beads 231 are formed in the inner panel 202 to be extended in the vehicle width direction. Between the beads 231, a joining point surface 232 as the joining surface to the outer panel 201 is provided. A lock reinforcing member 205 supporting a striker 206 is joined and fixed to the lower surface of the inner panel 202 at the vehicle front end.